The field of the present invention is nonstep hydrostatic transmissions.
Various nonstep transmissions have been disclosed. Reference is made to Japanese Patent Application Laid-Open No. 3-163253, Japanese Patent Application Laid-Open No. 2-113168 and Japanese Patent Application Laid-Open No. 4-203554, the disclosures of which are incorporated herein by reference.
A nonstep transmission according to Japanese Patent Application Laid-Open No. 3-163253 has a plurality of clutch valves radially arranged in a cylinder block in a manner to allow them to reciprocate in the radial direction of the cylinder block in engagement with a clutch control ring encircling the cylinder block. Such a transmission requires a large cylinder block with a large number of clutch valves. Inevitably such devices are heavy and require excessive manufacturing steps.
A nonstep transmission according to Japanese Patent Application Laid-Open No. 2-113168 has a clutch valve provided at the end of a shaft coaxially linked with a cylinder block. This arrangement requires an axially elongated transmission. Since the clutch valve is relatively wide with ring-shaped oil passages coaxially formed on its inner circumference and outer circumference, the flow resistance is large with a delay in response when the short-circuit flow of actuating oil is large in amount.
In Japanese Patent Application Laid-Open No. 4-203554, a nonstep transmission is disclosed which includes a pair of check valves compactly arranged inside a valve cylinder fitted in and fixed to the center of the cylinder block. This arrangement supplies actuating oil to ring-shaped oil passages coaxially formed on the inner circumference and outer circumference of the cylinder block. In the valve cylinder, a communicating hole is drilled in a position eccentric from the axes of the two check valves to communicate with oil supply passages formed on the two sides of the valve cylinder in the axial direction. Therefore, the thickness of the valve cylinder and its diameter become relatively large and the cylinder block is correspondingly large.